Conventionally, in the case where a large inductance load has to be actuated, a current supply control circuit is interposed between the inductance load and a high-voltage electrical power source so that an application of high voltage can be controlled by the current supply control circuit. For example, in order to realize a magnetic levitation of a rotor member in a magnetic bearing (i.e. a linear motor) using an electromagnet associated with a large inductance exciting coil, a high voltage is applied to the exciting coil so as to steeply build up an exciting current.
Furthermore, in a reluctance type motor with an exciting coil having a fairly large inductance for its armature, a voltage 5.about.10 times as large as a normal voltage for obtaining a normal motor output torque is applied to a current supply circuit during a building-up period of an exciting current in order to promptly build up the exciting current for preventing the motor output torque from being undesirably reduced. Also, a magnetic energy stored in the exciting coil is returned to an electric power source during a trailing-edge period of the exciting current, thereby quickly decreasing the exciting current to prevent a counter torque from being generated.
However, a voltage required for realizing a magnetic levitation of a rotor member in a magnetic bearing or a voltage applied to an exciting coil of a reluctance motor for building up an exciting coil are so large that a voltage of the electric power source becomes excessively large.
Furthermore, if an applied voltage to a reluctance motor is not sufficient, a building-up and a trailing-edge of an exciting current become so dull that not only a torque reduction appears in its building-up period but a counter-torque occurs in its trailing-edge period. This means that the motor cannot be driven at a high speed.
For example, in the case where a conventional reluctance type motor is driven by a battery as a driving source of an automotive vehicle, the rotational speed of the motor cannot be increased more than several hundreds rpm. Thus, the motor will not have any practical use. A stepping motor also has similar problems.